Method of producing guanidine nitrate



July 21, 1959 J. N. ROBINSON ET AL 2,895,994

METHOD OF' PRODUCING GUANIINE NITRATE Filed May 17, 1956 HNO?,

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' 4 Neuvguz/ATION STAGe AMMONIUM SULPHAMATG;

4 Al Robinson MLMz//er B. McDonnel/ /n ue ntors MW zzorn;

-covered lfrom the reaction mixture.

United States Patent() lMETHGD "F PRODUCING GUANIDINE This.. inventionrelates. to.- the production. of... guanidine nitrate-.andisparticularly directedA to an improved method for themanufacture ofguanidinenitrate-from readily available raw materials.

Guanidine nitrate is relatively well known and is-used in themanufacture of explosives and explosivemixtures, in disinfectants andphotographic chemicals.i It is a white granular substance having thechemical formula Guanidine nitrate is usually produced bych'emical'reactions in which cyanamide or dicyandiamide is an essentialconstituent, for` example, by reacting one of these compounds withammonium nitrate in themolten state atA elevated temperatures.

We have found that :guanidine nitrate can be produced in high yieldunder moderate temperature and'pre'ssure conditions in aqueoussolutions. The method'involves, in essence, the step of reactinglguanidine sulphamate with nitric acid to form guanidine nitrateand'sulphamic acid. Guanidine nitrate substantially free from impuritiesis re- Sulphamic acid also can be recovered.

Avery satisfactory method ofproducing guanidine sulph'amate is that ofreactingurea, sulphur dioxide, ammonia and ammonium sulphamate in aclosed reaction vessel at a temperature above atmospheric temperatureand under a superatmospheric pressure of ammonia. A reaction mixture isformed Iwhich contains a high yield of guanidine sulphamate. This methodof producing guanidine sulphamate has the important advantages ofmoderate operating conditions; it is relatively easily controlled toproduce a desired yield of guanidine sulphamate; the reaction mixture isin a uid condition andcan be removed from the reaction vessel withoutdiiculty and is readily amenable to treatment for the recoveryof thedesired end productor products; and the' methodis ideally adapted. foroperation on a continuous scale... The method makes use of relativelyinexpensive, readily available'. chemical compounds and is particularlywell adapted to the production of guanidine nitrate from guanidinesulphamate as the sulphamic acid by-product formed with guanidinenitrate can tbe neutralized to make ammonium sulphamate for use in thesynthesisv of guanidine' sulphamate.A

The method of producing guanidine nitrate is described yin detail inconjunction with the preferred method of producing guanidine sulphamatedescribed.. above.

1. Production of guanidine sulphamate'by synthesis The production ofguanidine sulphamate by reacting urea,y ammonia, sulphur dioxide'andammonium sulphamate'at a temperature above atmospheric temperature andunder a` superatmospheric pressure of added ammonia appears to involve aseries of complex reactions accom- 2,895,994 Patented July 21, 1959 2:3paniedby the formationof intermediate products but may be represented bythefollowing equatinz. 2CO(NH2)2+asozarzrunsoamrn+4NH3 2CNH(NH)27HSO3NH2+2.(NH4)2SO4+S The yield"offguanidiiiesulphamate yfrom this'reaction is high but the conversion isnotcornplete as a small amount ofcyclic products-'such as melamineand ammeline usually. is yfin-med;Inthenormal 'operation'offthemethod; thev yield of guanidinesulphamate-is about 85% of tlietlieoretiallbased on the ureapresent in'the reaction mixture.

In'operatingtliis step ofthe-method, thereactantsprcferably are,lpassedcontinuously"to` a reaction; vessel such as. an autoclave or tothe first of two autoclaves in series. The"temperature4 in the'reaction` vessel is maintained at from about 280 C. to about`330 C.,preferably at about 3.15.? C., and the-totalpressure iszmaintained.between about 400 and about` 1000 pounds per square inch. Thispressuresprovided bythe. addition of excess. ammonia to the reactionvessel. The total time of retention of the reaction mixture. in` the.reaction vessel; or vessels; may rang@ from"40, to160 minutes at 280 C.,and from 3 to l5 minutes at 330 C. At the preferred operating;temperature 'o.315! C., the:y preferred.. time of retention tins thereaction .vessel iszabout'.. 10 .to` 30Lminutes, for; example;l 10minutes' ineach. of two` autoclaves: in series...

In operating: thevmethodson; acontinuousbasis, .reaction mixture?spassed continuously from the autoclave-to. a coolingvessel where vthetemperature is reduced toiabout C.,.suchias byf reuxingexcessfammonia;and then to afpressurezreleaseves'sel where the pressure isreducedto-.atrnosph'eritxpressurezbyV release: of ammonia.. Ammonia-'.evolved;in the. coolingxand.` pressure release steps isrecovered and can.be-returnedto the process..

2.. Separation ofV guanidine sulphur/nale.y fromthe reaction mixtureVReaction mixture. from the pressure release vessel. is transferredtoaleaching tankwherein it is 'agitatedv in airstleachingstep.at.about-40"C. with an .aqueous solutionsaturated ataboutBO." C.with guanidinesulphamate and ,ammonium sulphate.l Guanidinesulphamate issepa ratedfromrthe reaction mixture by being dissolved. in the solution.The resulting solution is then separatedfrom undissolved. residue. whichcontains. sulphur. and cornpounds such as .melamine sulphate, ammoniumsulphate and. amineline. The. undissolved residue,A can be treatedtorecover. separatelyelemental -sulphur andany. of these compounds,. ifdesired.v

'Ihe solution.containingguanidine sulphamateis cooled to about 3'0 C. toprecipitate guanidine sulphamate and ammoniumsulphate .which can bey*separated `from the solutionby filtration or by centrifuging. Theguanidine sulphamate-ammonium. sulphate.. vsolution is re-cycledy tothefrstleachingstep.

The. mixture of guanidine sulphamateand ammonium sulphateseparatedfromthe rst leach solution is leached at about..40 C. in asecond leaching stepwith asolution saturatedat about 30 C..withguanidine sulphamate but unsaturatedlat 30 C. with respect to.ammoniumsulphate. The resultingfsolutonis thencooledtoabout 30 C. toprecipitate relatively, pure guanidine. sulphamate 1 without concurrent.precipitation. of ammonium sulphate. The precipitate and the. solutionare separated, such as by iiltration. or bycentrifuging, and. thesolution is returned to the second leaching,step,.aportionfbeing. bledolto control the ammoniumsulphate concentration.

The s'eparationof. guanidine sulphamate by a seriesof leaching andcooling steps at specified temperaturesuss Precipitated solid sulphamicacidis lGuanidine nitrate crystals are ing aqueous solutions ofspecified conce trations is very eiective for the production ofguanidine sulphamate in very pure form. We have found that a series oftwo leaching and cooling steps. is adequate in our method but furtherrepetitions inthe series can be carried out if extreme purity of theguanidine sulphamate salt is required.

asoman The operating temperatures for the leaching and cooling steps mayvary within relatively wide ranges. Temperatures in the range between 60C. and 20 C. are most satisfactory with a spread of from about ten totwenty degrees between the upper and lower operating temperatures beingmost desirable to ensure effective separation and crystallization of therequired products and economic operation. The dissolving temperature ofabout 40 C. and the precipitating temperature of about 3 0 C. suggestedabove are preferred conditions.

The conversion of guanidine-'sulphamate to guanidine nitrate is effectedby acidification with nitric acid. The

reaction can be expressed by the following equation:

Guanidine sulphamate obtained in the previous step is l ydissolved inwater in a rst dissolving step and, after -drawn from the vessel iscooled to about C. thereby precipitating guanidinenitrate which can berecovered readily by filtration. Water added to the acidification stepwith the guanidine sulphamate and the nitric acid dilutes the solutionsuciently to prevent crystallization of sulphamic acid on cooling toabout 30 C.

Filtrate from the separation of guanidine nitrate is evaporated at about5 0 C. to precipitate sulphamic acid. separated from the solution whichis saturated at about 5 0 C. with sulphamic acid and almost saturatedwith guanidine nitrate.

arated sulphamic acid is vpassed to a neutralization step described indetail hereinafter.

ie'aehed'in a third reaching step at about 30 C. with water and recycledguanidine This solution is cycled to the acidification step. Thesepnitrate solution; The resulting mixture is ltered to re- 'cover pureguanidine nitrate, which is dried and passed Ato storage. Thiscrystalline guanidine nitrate constitutes the product of theprocess, andis substantially free from impurities.

The filtrate from this second guanidine nitrate separation step isreturned partly to the third leaching step and partly to the acidicationstep.

Throughout the conversion stage of the method, solu- 'tion temperaturesare not permitted to rise above about 50 C. to 55 C. Temperaturesappreciably above this range cause excessive hydrolysis of sulphamicacid to sulphuric acid with a resulting loss of sulphamate forIrecycling to the synthesis stage of the process and diiculties inseparation of the various components in this stage of the process. Thetemperature difference of ten to twenty degrees between the uppertemperature and the precipitation temperature for guanidine nitrateensures that the separation is etective. Temperatures of ously, theupper temperature limit of about 551C. should 4not be exceeded. l l

Sulphamic acid crystals separated in the conversion stage are dissolvedin a second dissolving step in aqueous ammonium sulphamate solution towhich sucient am monia is added to neutralize the sulphamic acid, thusconverting the sulphamic acid to ammonium sulphamate. The temperatureduring neutralization is about C., maintained by the heat of reaction.

The resulting solution is cooled to about 30 C. to precipitate ammoniumsulphamate which can be separated from the solution, such as byfiltration or by centrifuging. The solution is returned to the seconddissolving step.

Solid ammonium sulphamate is dried and returned to the synthesis stageof the process. This recycle of ammonium sulphamate results in a directsaving of sulphur dioxide and ammonia equivalent to the sulphamic acidproduced.

The temperatures of about 80 C. and about 30 C. are preferred in thesteps of the neutralization stage of the process, but other temperaturescan be used provided that there is a sufficient difference between theupper and lower temperatures to ensure effective and economic separationof ammonium sulphamate.

The preferred materials employed in the construction jof the leachingvessels and anchillary apparatus in contact with the reaction mixturesthroughout the separation, conversion' and neutralization stages of theprocess are stainless steel and aluminum.

In the synthesis stage, the reaction mixture is very corrosive,particularly at temperatures above about C.l Equipment such as thereaction vessel and cooling vessel is preferably made of stainless steellined with a corrosionresistant material such as carbon or tantalum.

The following example illustrates, in conjunction with the attached owsheet drawing, the operation of the process.

About 43 pounds of rurea, 77 pounds of sulphur dioxide, 60 pounds ofammonia and 64 pounds of amjmonium sulphamate are fed per minute intothe synthesis stage, indicated by the numeral l in the attached flowsheet drawing. These materials are reacted at a temperature of about 315C. and under a total pressure -of ammonia of from about 500 to 600pounds per square inch for a period of about 30 minutes, producing areaction mixture which contains about 91 pounds of guanidine sulphamate,98 pounds of ammonium sulphate, 6 pounds of melamine sulphate, 0.8 poundof ammeline, 14 pounds of sulphur and 0.8 pound of urea. Approximately34 pounds of ammonia are released during the cooling and pressurerelease steps of this stage and returned to the synthesis stage. Thereaction product is passed to the separation stage, indicated by thenumeral 2, wherein guanidine sulphamate is separated from the reactionproduct. The residue from this separation stage contains about 4 poundsof guanidine sulphamate, about 98 pounds of ammonium sulphate, about 2pounds of melamine sulphate, about 0.8 pound of urea, about 13 pounds ofsulphur, about 0.6 pound of ammeline and about 5 pounds of water.

Guanidine sulphamate recovered from the separation stage is passed totheconversion stage, indicated by the numeral 3, wherein it is reacted withabout 64 pounds of 55% nitric acid. The guanidine nitrate productrecovered from this stage contains about 67 pounds of',g'uanidine,nitrate,V less than 0.05 pound of ammonium sulphate, about0.6 'pound of melamine sulphate, less than 0.01 pound of urea, about0.05 pound of sulphamic acid and a minute amount of water. That is, theresulting guanidine nitrate product is of about 99% purity.

Snlphamic acid recovered from the conversion stage is neutralized withammonia in a neutralizing stage, indicated by the numeral 4, to produceammonium sulphamate. About 64 pounds of ammonium sulphamate containingabout 2 pounds of impurities are recovered from the neutralization stageand returned to the synthesis stage. Suficient ammonium sulphamate isformed in the neutralizing stage to effect a substantial saving in theamount of sulphur dioxide and ammonia which otherwise would have beenrequired for the synthesis stage.

The yield of guanidine nitrate recovered from the process when operatingunder the above described conditions is of the order of about 77.5% ofthe theoretical yield based on the amount of urea employed in thesynthesis step.

The process of the present invention possesses a number of importantadvantages. The reaction between guanidine sulphamate and nitric acid isconducted at a relatively low temperature in aqueous solution withoutdanger of explosion and with a satisfactory yield of guanidine nitrateof high purity. Guanidine nitrate is easily separated and recovered fromthe reaction product. The preferred method of making guanidinesulphamate is ideally adapted for use as a step in the overall processin that a high yield of guanidine sulphamate can be produced on acontinuous basis under moderate temperature and pressure conditions. Thereaction mixture from this step is in Huid condition and can bewithdrawn without diculty from the reaction vessel. Sulphamic acidproduced in the guanidine sulphamate-nitric acid conversion step iseasily converted to ammonium sulphamate which is cycled to the guanidinesulphamate synthesis step of the overall process effecting substantialsavings in the ammonia and sulphur `dioxide which otherwise would berequired for that step of the process.

It will be understood, of course, that modifications can be made in thepreferred embodiment of the invention described herein without departingfrom the scope of the invention as defined by the appended claims.

What we claim as new and desire to protect by Letters Patent of theUnited States is:

1. ln a process for the production of guanidine nitrate in whichammonia, sulphur dioxide, urea and ammonium sulphamate are reacted toproduce a reaction product which contains guanidine sulphamate,guanidine sulphamate is separated from the reaction product and isreacted with nitric acid to form a reaction product which containsguanidine nitrate and sulphamic acid, the im provement which comprisesseparating and separately recovering guanidine nitrate and sulphamicacid from the guanidine nitrate-sulphamic acid reaction product,neutralizing recovered sulphamic acid with ammonia to form ammoniumsulphamate, and re-cycling so-formed ammonium sulphamate to theguanidine sulphamate forming step of the process.

2. The process for the production of guanidine nitrate according toclaim l characterized in that the guanidine sulphamate-nitric acidreaction is conducted at a temperature below about C.

3. The process for the production of guanidine nitrate according toclaim l characterized in that the guanidine sulphamate-nitric acidreaction is conducted in a cycling solution which contains sulphamicacid and guanidine nitrate at a temperature below about 55 C. and abovethe saturation temperature of the `cycling solution of sulphamic acidand guanidine nitrate, and guanidine nitrate and sulphamic acid areprecipitated from the cycling solution in the order named bycrystallization.

References Cited in the le of this patent UNITED STATES PATENTS2,464,247 Mackay Mar. 15, 1944 2,653,976 Mackay Sept. 29, 1953 2,698,344Mins Dec. 2s, 1954 2,762,843 Boivin Sept. 11, 1956 2,768,203 HamiltonOct. 23, 1956 FOREIGN PATENTS 162,088 Australia Sept. 10, 1953 705,799Great Britain Mar. 17, 1954

1. IN A PROCESS FOR THE PRODUCTION OF GUANIDINE NITRATE IN WHICHAMMONIA, SULPHUR DIOXIDE, UREA AND AMMONIUM SULPHAMATE ARE REACTED TOPRODUCE A REACTION PRODUCT WHICH CONTAINS GUANIDINE SULPHAMATE,GUANIDINE SULPHAMATE IS SEPARATED FROM THE REACTION PRODUCT AND ISREACTED WITH NITRIC ACID TO FORM A REACTION PRODUCT WHICH CONTAINSGUANDINE NITRATE AND SULPHAMIC ACID, THE IMPROVEMENT WHICH COMPRISESSEPARATING AND SEPARATELY RECOVERING GUANDINE NITRATE AND SULPHAMIC ACIDFROM THE GUANIDINE NITRATE-SULPHAMIC ACID REACTION PRODUCT, NEUTRALIZINGRECOVERED SULPHAMIC, ANDF RE-CYCLING SO-FORMED AMMONIUM SULPHAMATE TOTHE GUANIDINE SULPHAMATE FORMING STEP OF THE PROCESS.